The present invention relates to a clean bench for preventing occurrence of a hazard which is caused through treatment of microorganisms or pathogenic organisms during genetic manipulation for medical treatment, pharmaceutics or the like, that is, it relates to a safety cabinet for countermeasures to biohazards.
Heretofore, there has been used, as a countermeasure for biohazards, a safety cabinet which isolates microorganisms or pathogenic organisms from a human body or an environment. As to this safety cabinet, there may be used a safety cabinet of a biohazard countermeasure class II type which satisfies or conforms to JIS K3800. This cabinet is provided with an openable front shutter which is opened for accessing a working space defined in the cabinet in order to set or remove a laboratory instrument into or from the working space. JIS K3800 stipulates that no air stream leaks by way of rail parts at upper and lower side edges of the front shutter and by way of a seal wiper at the upper side edge thereof. In an example of the configuration of a conventional safety cabinet, the seal wiper is provided against the inner surface of the shutter so as to prevent leakage of any air stream and entrance of microorganisms into the working space from the outside and as well to prevent leakage of microorganisms and pathogenic organisms from the working space to the outside.
FIGS. 7a to 8b show an example of the configuration of a conventional safety cabinet, that is, FIG. 7a is a vertical sectional view illustrating the safety cabinet, FIG. 7b is a partly broken front view thereof, FIG. 8a is an enlarged vertical sectional view illustrating a part of the safety cabinet around a front shutter 9 and FIG. 8b is an enlarged cross-sectional view thereof. Referring these figures, there are shown the safety cabinet 1′ a workbench 2, a working space 3, an exhaust air HEPA filter (High Efficiency Particulate Air filter) 4, an intake air HEPA filter 5, a blower 6, a blow-off rectifying vanes 7, a seal wiper 8, the front shutter 9, blow-off air 12, inflow air 13, a positive pressure contamination plenum 14, a negative pressure contamination plenum 15, and an air suction port 18. The inflow air 13 sucked into a space below the front shutter 9 flows below the workbench 2 and in rear of the working space 3, and then sucked into the blower 6. The thus sucked air is mixed therein with biological specimens and pathogenic organisms which have been treated in the working space 3. The pressure in the air introduction part on the suction side of the blower 9 becomes negative, and accordingly, the biological specimens and the pathogenic organisms are sucked thereinto. Thus, the space 15 where negative pressure air contaminated with the biological specimens and the pathogenic organisms flows is the so-called negative pressure contamination plenum 15. Further, air blown off from the blower 6 is fed into the closed space 14 in which the air is pressurized by the blower 6 so as to have a positive pressure, and is contaminated with the biological specimens and the pathogenic organisms and which is therefore the so-called positive pressure contamination plenum 14. The positive pressure air from the positive pressure contamination plenum 14 is filtered by the intake air HEPA filter 5 so as to be turned into purified blow-off air 12 which is fed into the working space 3. The blow-off air 12 to be fed into the working space 3 is rectified by the flow-off rectifying vanes 7 for uniform distribution of blow-off velocities. The inflow air 13 sucked into the opening of the working space 3 below the front shutter 9 and the blow-off air blown off through the rectifying vanes 7 flow through the negative pressure contamination plenum 15. Then, a part thereof is filtered by the exhaust air HEPA filter 4 so as to remove dust and dirt including the biological specimens and the pathogenic organisms and is then discharged outside of the safety cabinet 1′. The exhaust air HEPA filter 4 has two roles, that is, filtering air from the positive pressure contamination plenum 14 into which air is fed by a positive pressure of the blower 6 and discharging the same outside of the safety cabinet 1′, and filtering air in the safety cabinet 1′ into which air is fed by way of the negative pressure contamination plenum 15 by a blower (which is not shown) provided outside of the plenum, and discharging the same outside of the safety cabinet 1′. The worker who treats the biological specimens and the pathogenic organisms looks into the working space 3 through the intermediary of the front shutter 9, and inserts his hands thereinto through the opening below the front shutter 9 so s to carry out the treatment thereof within the working space 3. The seal wiper 8 is provided between a partition wall defining the working space 3 and the front shutter 9 so as to prevent inflow of the outside air into the working space 3 and flow-out of the inside air from the safety cabinet 1′. Air suction ports 18 are provided on opposite sides of the opening below the front shutter 9 in order to prevent disturbance of air streams both sides of the opening. Further, the front shutter 9 is inclined by an angle of about 10 deg. with respect to a vertical plane in order to facilitate observation into the working chamber 3 by the worker. Either of JP-B2-2,883,420, JP-A-6-297356 and JP-A-2000-346418 discloses a safety cabinet having a front shutter 9 provided thereto with a means for preventing inflow of the outside air and outflow of the inside air. Specifically, JP-B2-2,883,420 discloses such a configuration that a seal wiper is provided between the front shutter and a partition wall of the working space so as to keep gas-tightness, and JP-A-6-297356 discloses a workbench in which negative pressure is effected in a coupling part between an air supply/discharge unit and a working chamber unit, and an air volume is adjusted by a damper in the air supply/discharge unit so as to introduce the outside air into the working chamber unit while JP-A-2000-346418 discloses such a configuration that negative pressure is effected in a negative pressure air intake passage within a suction duct which is provided in the inner peripheral edge of a glass window in a partition wall defining a working space so as to cause air in the isolator to flow into the suction duct from a suction port through an air-permeable seal packing in order to prevent the air in the isolator from leaking into the outside at the periphery of the window.
Further, the worker who carries out experiments with the use of a safety cabinet, and who inserts his hands in the working space through the front opening in order to carry out the experiments, has to hold his hands for a long time until the experiments is completed, and accordingly, he is tired so as to rest his hands on the bottom surface of the workbench, resulting in blockage of air-suction ports. This causes disturbance of air streams, and as a result, the biological specimens and the pathogenic organisms leak outside of the safety cabinet from the working space, or various germs enters into the working chamber from the outside through the opening so as to cause contamination.
JP-A-2002-079118 discloses a workbench having arm holders for resting the arms at predetermined positions in order to prevent the dropped arms from blocking the air suction ports.
JP-B2-2,577,751 discloses a workbench which is provided at its front face with protrusions so that the front opening is located at a level higher than the bottom surface of the workbench in order to prevent the arms from blocking the air-suction ports even though the arms are dropped onto the bottom surface of the workbench.
Of these above-mentioned conventional safety cabinets, the safety cabinet shown in FIGS. 7a to 8b, has the seal wiper 8 made of rubber or resin, and accordingly the seal wiper 8 is likely to be readily damaged due to a friction between itself and the front shutter. If it is damaged, entrance of the outside air and leakage of air from the inside to the outside of the safety cabinet cannot be avoided. Thus, the seal wiper 8 should be periodically replaced with new one. Further, since the air suction ports 18 are merely provided at both side ends of the opening below the front shutter 9, there cannot be prevented both occurrence of turbulence in the corner parts between the front shutter 9 and the side surfaces 3a′ of the working space 3, and leakage of air through the rails 10 for the front shutter 9.
Further, there may be a possibility of leakage of air from corner parts between the shutter rails 10 and the seal wiper 8 at the upper end of the partition wall of the working space 3. Further, the front shutter 9 is inclined at its front surface by an angle of 10 deg. with respect to a vertical plane. Burble due to the inclined structure of the front shutter 9 is caused within the working space 3. In general, it has been known that the space which is widened in the flowing direction causes air to peel off along the inner wall parts of the passage if the passage is widened on both sides thereof by an angel of not less than about 4 to 5 deg. (about 2 to 2.5 deg on one side). In order to prevent air from peeling off, such a countermeasure that the velocities of air streams 12 blown off around the front shutter 9 are increased is taken. This countermeasure causes an increase in the velocity of the air in the working space 3 around the front shutter 9, and as a result, air is more likely to leak from the upper part of the front shutter 9 and around the front shutter rail 10 at both sides of the front shutter 9. Further, in the configurations of the safety cabinets disclosed in JP-B2-2,883,420 and JP-A-2000-346418, the gas-tightness of the working space is held or air in the isolator is prevented from leaking outside thereof, and accordingly, seal packing is required between the front shutter or the glass window and the partition wall of the working space. Further, JP-A-6-297356 discloses the configuration of a clean workbench in which the working chamber unit and the supply/discharge unit are fastened to each other, which effects negative pressure for preventing leakage of contaminants from the supply/discharge unit caused by the fastening structure, but this configuration is not the one which prevent leakage of air or entrance of air around the front shutter in the working chamber unit.
Further, in the above-mentioned conventional safety cabinet (JP-B2-2,883,420), the arm holders provided in front of the workbench hinder laboratory instruments from being brought into and out from the working space. Further, there has been raised a problem of inferior work efficiency of sterilization or disinfection for protrusions of the arm holders provided in front of the workbench.
FIG. 17 shows in detail the front opening of the conventional safety cabinet. When the worker inserts his arms into the working space so as to treat biological specimens or pathogenic organisms in the safety cabinet, the arms 101′ are extended into the working space 3 from the center part of the front opening 64 so that the air streams 92′ wrap around the arms while the air is sucked from the working space 3 and the outside of the safety cabinet through suction slits 66′ (See dotted lines in FIG. 17). If experiments carry out for a long time so as to tire the worker who drops his arms 101′, the arms 101′ abuts against the inlet opening part 67′ of the working bed, and accordingly, it does not directly block the suction slits 66. In general, the workbench 2′ has a height which is set to 750 mm in view of easily execution of experiments and the working efficiency for the human. However, the conventional safety cabinet shown in FIG. 17 has the inlet part 67 which is higher than the working surface of the workbench by 30 to 40 mm, resulting in discomfortability during working.